Re: [PATCH 1/5] Poison non-POD memset & non-trivially-copyable memcpy/memmove

[Pedro Alves <palves@redhat.com>]

On 04/25/2017 10:24 AM, Pedro Alves wrote:
> On 04/25/2017 09:24 AM, Yao Qi wrote:
>> Pedro Alves <palves@redhat.com> writes:
>>
>> Hi Pedro,
>>
>>> +/* True if "T *" is relocatable.  I.e., copyable with memcpy/memmove.
>>> +   I.e., T is either trivially copyable, or void.  */
>>> +template<typename T>
>>> +struct IsRelocatable
>>> +  : gdb::Or<std::is_void<T>,
>>> +	    std::is_trivially_copyable<T>>
>>> +{};
>>
>> This breaks the build with gcc 4.8,
>>
>> In file included from ../../binutils-gdb/gdb/common/common-defs.h:85:0,
>>                  from ../../binutils-gdb/gdb/defs.h:28,
>>                  from ../../binutils-gdb/gdb/gdb.c:19:
>> ../../binutils-gdb/gdb/common/poison.h:66:6: error: ‘is_trivially_copyable’ is not a member of ‘std’
>>       std::is_trivially_copyable<T>>
>>       ^
>>
> 
> Sorry, I thought I had tested gcc 4.8, but clearly I did not.  I'll fix it
> as soon as I have a chance, probably by disabling the poisoning on
> older compilers.

Like this.  I went ahead and pushed it.

From debed3db4887483552103da36d180967ef0dca5f Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Tue, 25 Apr 2017 10:58:57 +0100
Subject: [PATCH] Fix build on gcc < 5 (std::is_trivially_copyable missing)

Ref: https://sourceware.org/ml/gdb-patches/2017-04/msg00660.html

Simply skip the poisoning on older compilers.

gdb/ChangeLog:
2017-04-25  Pedro Alves  <palves@redhat.com>

	* common/poison.h [!HAVE_IS_TRIVIALLY_COPYABLE] (IsRelocatable)
	(BothAreRelocatable, memcopy, memmove): Don't define.
	* common/traits.h (__has_feature, HAVE_IS_TRIVIALLY_COPYABLE): New
	macros.
---
 gdb/ChangeLog       |  7 +++++++
 gdb/common/poison.h |  4 ++++
 gdb/common/traits.h | 13 +++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 26e6370..d1c1942 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,12 @@
 2017-04-25  Pedro Alves  <palves@redhat.com>
 
+	* common/poison.h [!HAVE_IS_TRIVIALLY_COPYABLE] (IsRelocatable)
+	(BothAreRelocatable, memcopy, memmove): Don't define.
+	* common/traits.h (__has_feature, HAVE_IS_TRIVIALLY_COPYABLE): New
+	macros.
+
+2017-04-25  Pedro Alves  <palves@redhat.com>
+
 	* common/common-defs.h: Include "common/poison.h".
 	* common/function-view.h: (Not, Or, Requires): Move to traits.h
 	and adjust.
diff --git a/gdb/common/poison.h b/gdb/common/poison.h
index a875568..37dd35e 100644
--- a/gdb/common/poison.h
+++ b/gdb/common/poison.h
@@ -55,6 +55,8 @@ template <typename T,
 	  typename = gdb::Requires<gdb::Not<IsMemsettable<T>>>>
 void *memset (T *s, int c, size_t n) = delete;
 
+#if HAVE_IS_TRIVIALLY_COPYABLE
+
 /* Similarly, poison memcpy and memmove of non trivially-copyable
    types, which is undefined.  */
 
@@ -80,4 +82,6 @@ template <typename D, typename S,
 	  typename = gdb::Requires<gdb::Not<BothAreRelocatable<D, S>>>>
 void *memmove (D *dest, const S *src, size_t n) = delete;
 
+#endif /* HAVE_IS_TRIVIALLY_COPYABLE */
+
 #endif /* COMMON_POISON_H */
diff --git a/gdb/common/traits.h b/gdb/common/traits.h
index 4f7161b..8c41b03 100644
--- a/gdb/common/traits.h
+++ b/gdb/common/traits.h
@@ -20,6 +20,19 @@
 
 #include <type_traits>
 
+/* GCC does not understand __has_feature.  */
+#if !defined(__has_feature)
+# define __has_feature(x) 0
+#endif
+
+/* HAVE_IS_TRIVIALLY_COPYABLE is defined as 1 iff
+   std::is_trivially_copyable is available.  GCC only implemented it
+   in GCC 5.  */
+#if (__has_feature(is_trivially_copyable) \
+     || (defined __GNUC__ && __GNUC__ >= 5))
+# define HAVE_IS_TRIVIALLY_COPYABLE 1
+#endif
+
 namespace gdb {
 
 /* Pre C++14-safe (CWG 1558) version of C++17's std::void_t.  See
-- 
2.5.5